Volume 3, Issue 2, July 2010

Studies on frequency chirping in optically illuminated a-Gallium Nitride Impatt Diodes at Sub-millimeter wave frequency  [Full Text]

Soumen Banerjee, Department of Electronics & Communication Engg, Hooghly Engineering & Technology College, Hooghly, WB, India
Priya Chakrabarti is with the Institute of Engineering & Management, Kolkata, India
Riya Baidya is with the Institute of Engineering & Management, Kolkata, India
J. P. Banerjee is with the Institute of Radio Physics & Electronics, University of Calcutta, Kolkata, India

The frequency chirping effect under optically illumination of Wurtzite phase of Gallium Nitride (Wz-GaN or a-GaN) based DDR Impatt diodes at 300 GHz or 0.3 Terahertz (THz) has been investigated. Top Mounted (TM) and Flip Chip (FC) structures are chosen and the composition of photocurrent is altered by shining light on the p+ side and n+ side of the device through optical windows. A double iterative computer simulation method based on drift-diffusion model has been used to study the small signal performance and subsequent modification of the small signal parameters owing to optical illumination. The role of leakage current in controlling the dynamic properties is studied by varying the current multiplication factors for electrons (Mn) and for holes (Mp). The simulation studies reveal that these devices are potential sources for generating high power at Terahertz domain. The conversion efficiency is found to be 15.47% at 0.3 THz at an optimum bias current density of 0.5 x 108 A/m2. The output power obtained is 6.23 W at 0.3 THz. The optical illumination reveals that a lowering of Mp causes more upward shift in frequency than a corresponding lowering of Mn. The frequency chirping in a-GaN Impatt is of the order of few GHz. The design results thus indicate the high photo-sensitiveness of a-GaN Impatts at Terahertz domain.


Analysis of MISO WIMAX IEEE802.16d in SUI Multipath Fading Channels
  [Full Text]

Mohammed Aboud Kadhim, School of Electrical and Electronics Engineering, Universiti Sains Malaysia, Seri Ampangan, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia
Dr.Widad Ismail, School of Electrical and Electronics Engineering, Un-iversiti Sains Malaysia, Seri Ampangan, 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia

This paper presents a physical scattering model that predicts multiple-input multiple-output (MIMO) channel characteristics con-forming well to experimental observations in WIMAX IEEE802.16d. Our approach is to start with a given single-input single-output power-delay profile (defined for specific range, bandwidth and antenna parameters) and fit a scattering model that characterizes the MIMO channel. From the derived scattering model and antenna array configurations. Simulations of SUI MIMO channels are shown to observed channel correlations, antenna beamwidth effect, range dependency, and frequency selectivity.


Perforated Reflect-Array Antennas
  [Full Text]

Mohammad Khalaj-Amirhosseini is with Iran University of Science and Technology, Tehran, Iran
Mojtaba Moeini-Fard is with Iran University of Science and Technology, Tehran, Iran

A new reflectarray antenna structure is proposed. This structure utilizes a perforated dielectric layer as a reflecting surface with the lattice of different holes. The effective permittivity of the dielectric substrate is altered by drilling holes with different diameter and spacing, which simulate an inhomogeneous dielectric layer. This inhomogeneous dielectric layer can be controlled by these holes to collimate the reflected waves in the special direction. Absence of resonator elements in this structure will reduce the dielectric and conductor losses, which are the main losses in reflectarray antennas at resonance frequency. The reflection properties of the perforated substrate versus their holes diameter and spacing between them are calculated by using the method of Finite Difference Time Domain (FDTD), in which an infinite periodic model was employed to obtain the reflected phase curves. Some proposed antennas are designed at millimeter wave frequency and simulated by full-wave analyzer; CST Microwave Studio software.


A Novel Routing Strategy for Ad Hoc Networks with Selfish Nodes 
[Full Text]

Shailender Gupta is with YMCA University of Science and Technology, Faridabad, India
Chander Kumar is with YMCA University of Science and Technology, Faridabad, India

To secure the data in the ad hoc network the intermediate nodes with in a route are created on the basis of their currently known reputation (trust) index. However, a node which was earlier trust worthy may no longer to be so as it becomes selfish due to loss of power. This selfish behavior problem is quite common in ad hoc networks and the literature contains many strategies to deal with them. This paper presents a novel routing strategy to deal with such nodes. The strategy assumes that the selfish nodes are not malicious and obligated to speak truth about their current energy level.


A Compact Ultra-Wideband Printed Spiral Slot Antenna with Band-Notched Characteristics
  [Full Text]

Nima Bayatmaku, Department of Electrical Engineering, Islamic Azad University Science and Research Branch, Tehran, Iran
Mohammad Naser-Moghadasi, Department of Electrical Engineering, Islamic Azad University Science and Research Branch, Tehran, Iran
Mohammad Jahanbakht, Electrical Engineering Department, Islamic Azad University, Shahr-e-Qods Branch, Iran
Bal S. Virdee is with Faculty of Computing, London Metropolitan University, London N7 8DB, UK

A novel ultra-wideband microstrip antenna with a frequency notched characteristic is presented and investigated. The band-notched characteristic is achieved by embedding a spiral slot within the circular patch. The frequency of the notch can be precisely controlled by adjusting the length of the spiral slot. Simulation measured results show the antenna to operate over a frequency range of 2.6 to 11GHz, and it rejects interfering frequencies between 5.2 to 6.1 GHz corresponding to WLAN band.


Progress on TCP Fairness Achievement in IEEE 802.11 Infrastructure WLAN
  [Full Text]

Mohamed Othman and Tareq Rasul, Department of Com-munication Technology and Network, Faculty of Computer Science and In-formation Technology, Universiti Putra Malaysia, 43300 Serdang, Selan-gor D.E., Malaysia

TCP unfairness has becomes pronounced in IEEE 802.11 Wireless Local Area Networks (WLANs) due to the channel access competition and congestion in between two different medium (wired and wireless). In this paper, we focus on the TCP fairness issues that review from the three aspects; fairness among flow, station and rate. Due to the strong drive towards Internet access via wireless devices, these issues must be carefully handled in order to build improved systems. We briefly review the progress and categorize the TCP fairness characteristic and then outline the problems and solutions from previous works through a comparative table. Finally, we considered the future direction for solving these problems. Overall this paper summarizes current state of knowledge of the WLAN TCP fairness.


Wavelet Packet with Carrier Frequency Offset in OFDM Systems
  [Full Text]

Haitham J. Taha, School of Electrical & Electronic Engineering, Universiti Sains Malaysia, Seri Ampangan, 14300 Nibong Tebal, Pulau Pinang, Malaysia

Orthogonal frequency division multiplexing (OFDM) is an important multiple access candidate for 4G wireless communication system. While OFDM provides high performance and high capacity in frequency selective fading channels, OFDM is very sensitive to frequency errors caused by frequency differences between transmitter and receiver local oscillators. OFDM suffers from intercarrier interference (ICI) in the absence of precise frequency synchronization. The loss of orthogonality among subcarriers causes ICI which affects both channel estimation and detection of OFDM data symbols. Channel estimation error degrades the performance of coherent receiver limiting capacity, data rate and performance of the overall OFDM system.
In this paper we demonstrate the operation of a Wavelet Packet based OFDM modulation (WP-OFDM) scheme, and analyze the impact of interference in WP-OFDM transmission caused by the carrier frequency offset. The sensitivity of WP-OFDM transceivers to these errors using standard wavelets is evaluated through simulation studies and their performances are compared with FFT-OFDM. The proposed method can improve the performance of the system by estimating fine frequency offset. The simulation results show that there is satisfactory improvement in BER performance of the present scheme.


Periodically Loaded Rectangular Waveguide with FSS Strip Layer Supporting Wideband Backward Wave
  [Full Text]

A.Akbarzadeh-Jahromi, Electrical Engineering Department, Iran University of Science and Technology UniversityTehran, Iran
M.Tayarani, Electrical Engineering Department, Iran University of Science and Technology UniversityTehran, Iran
M.Khalaj-Amirhosseini, Electrical Engineering Department, Iran University of Science and Technology UniversityTehran, Iran

In this paper, a negative refractive index guided-wave structure is realized using a rectangular waveguide loaded with H-shaped frequency selective surface (FSS) strip layer. This new structure shows wideband double negative (DNG) and backward wave properties. Indeed these properties can be controlled well over wide frequency range with control of physical dimension of the structure. Using the FSS, two wideband band-pass filter proposed which are inexpensive to fabricate due to using printed layer which are ideal for mass production.


Increasing Bit Rate using Adaptive Convolutional Codes and Mapping
  [Full Text]

Aseel Hameed Al-Nakkash, College of Electrical and Electronics Techniques

The big challenge for mobile communication system is to transmit large quantities of data . The criterion for the change of code rate is to maximize the throughput under given error bound. In this paper we present a flexible and low complexity variable rate convolutional codes when puncturing technique was adopted. Depending on variable Rate compatibility Puncturing Convolutional Codes (RPCC), we succeed to present an automatic system that finding the optimal channel coding architecture for different source bit rates and channel condition. . Simulation results show that good performance can be achieved on both Adaptive White Gaussian Noise (AWGN) and Ralyeih fading channels and we can still employ the same viterbi decoder for the convolutional mother code by using approximated metrics without increasing the complexity of the decoding operation.


Resource reservation using bandwidth in MANETS for swarm intelligence algorithm: Termite
  [Full Text]

F.ASharvani.G. S is with the R.V.C.E Bangalore-560059
S.B. Dr.T.M.Rangaswamy. is with the R.V.C.E, Bangalore-560059
T.C, Sudarshan HP is with the R.V.C.E Bangalore-560059
F.D, ,Keerthi Kiran is with the R.V.C.E Bangalore-560059
F.E Pavan Kumar VV is with the R.V.C.E Bangalore-560059
F.F Thandeep is with the R.V.C.E Bangalore-560059

This paper considers the bandwidth reservation problem in a mobile ad hoc network (MANET) to support QoS(quality-of-service) in termite Routing protocol. We use TDMA (Time Division Multiple Access) as controlled access to reserve the common channel between nodes. Multi media communication demands minimum bandwidth between nodes, this resource reservation using Termite routing protocol ensures the above said bandwidth criteria. However QoS has not been implemented in Termite Routing protocol. Here we propose an algo-rithm for QoS(Bandwidth) routing in the same.


OFDM-MIMO Technology for Spectrum Efficient Wireless Networks
[Full Text]

Nirmalendu Bikas Sinha, Department of ECE and EIE , College of Engineering & Management, Kolaghat, K.T.P.P Township, Purba- Medinipur, 721171, W.B., India

The use of multiple antennas at both transmitter and receiver to form multiple input and multiple output (MIMO) channels currently hold the potential to drastically improve wireless links spectrum efficiency or robustness, increasing capacity and the ability to increase the transmission speed in future wireless communications system as well as radar. For broadband communications, OFDM turns a frequency selective channel into a set of parallel flat channels, which significantly reduces the receiver complexity. Problems in multipath fading and interference are severe on road condition and environment also so dynamic. Existing wireless system may be utilized single frequency, single antenna and pulse for multicarrier transmission and reception. Problems of such system are that in case of failure the total system will become non-operational. A distributed system in terms of multicarrier, multiantenna., MIMO-OFDM jointly exploits the advantages of these two individual strategies. It therefore seems to be an attractive solution for future broadband wireless systems. Thus with the advent of MIMO assisted OFDM systems, transmission rate, transmission range and the transmission reliability may be simultaneously improved. The performance analysis for the MIMO-OFDM system has been carried out based on MATLAB simulation. The experimental results have been verified using the simulation, the results of simulation have been verified with the various works being carried out in this area and the results conferred to be correct.